In Australia, the trees, branches and other pieces of naturally occurring wood found in a sunken form in rivers and streams are called snags.

Snags are absolutely critical as shelter and spawning sites for native fish, and are critical as one of the few hard substrates available for biofilm growth and aquatic invertebrates in lowland rivers flowing through alluvial flood plains. Snags are critical as sites for biofilm growth and for shelter and feeding of aquatic invertebrates in both lowland and upland rivers/streams.

Unfortunately there has been massive ignorance of the roles of snags until recently and more than one million snags have been removed from the Murray-Darling river system. Large tracts of the lowland reaches of the Murray-Darling system are now devoid of the snags that icon native fish like Murray Cod need for shelter and breeding. The damage this snag removal has caused is massive and incalculable.